EXHAUST PROCESS and EMISSIONS

Transcription

1 Internal Combustion Engines MAK 493E EXHAUST PROCESS and EMISSIONS Prof.Dr. Cem Soruşbay Istanbul Technical University Internal Combustion Engines MAK 493E Exhaust Process in Engines and Emissions Introduction Exhaust process phases Gas flow rate and temperature variation Exhaust emissions 1

2 Introduction After combustion is completed and resulting high pressure gases have been used to transfer work to crankshaft during expansion stroke, these gases are removed from the cylinder in two steps : exhaust blowdown which is followed by exhaust stroke valve overlap The resulting flow in the exhaust pipe is a non-steady state pulsating flow. Introduction p 4 o (EgA) p r p e p r p a p e r 5 o (EmA) o 6 (EgK) 1 o (EmK) e ÜÖN AÖN V 4 6 Egzoz süpab aç k (EmA) 5 o o 1 (EmK) Krank dairesi ÜÖN (EgK) α=0-40 α=0-40 o 6 α=5-90 α= o AÖN (EgA) 5 1 Emme süpab aç k 2

3 Introduction Blowdown phase when exhaust valve opens towards the end of power stroke (60 40 o BBDC) cylinder pressure is about MPa and temperature up to 1000 K, while pressure in exhaust system is one atm. pressure difference causes rapid flow of exhaust gases from cylinder blowdown phase. flow at first is choked and outflow will be sonic With increasing engine speed, crank angle duration of blowdown phase increases Introduction Displacement phase (exhaust stroke) mass flow is controled by piston movement from BDC to TDC pressure is slightly above atm pressure closing of the valve starts at or close to TDC and the total closing is at 8 50 o ATDC Valve overlap intake valve starts to open o BTDC valve overlap o CA there can be reverse flow into cylinder : inc residual gases, which is worst at low speeds and idle short circuit of intake air/fuel mixture inc pollution 3

4 Temperatures SI engines exhaust gas temp o C average o C at idle and 900 o C at max power when exhaust valve opens, in cylinder gas temperature is o C more CI engines o C average cooling occurs due to larger expansion in Diesel engines Pollutant Formation IC engine exhaust gases contain oxides of nitrogen (NO and some amounts of NO2 collectively known as NOx), carbon monoxide (CO) and unburned hydrocarbons (HC). Soot and PM in Diesel engines. The amounts depend on engine design and operating conditions. These pollutants are measured as concentrations; CO, CO 2, O 2 as vol. [%] NO, NO 2, NO x as [ppm] (parts per million) HC as [ppm] or [ppm C] eg 1 ppm propan, C 3 H 8 3 ppm C 4

5 Control of Pollutant Emissions Combustion related applications : EGR (Exhaust gas recirculation) Water and alcohol injection Exhaust gas treatment : Thermal reactors Catalytic converters Traps and filters EGR system 5

6 EGR control Exhaust Gas Treatment Thermal reactors Require high temperatures, oxygen availability, sufficient time for reactions. Used for oxidation of CO and HC Rich mixture + O2 supplement : CO oxidation in exhaust system increases T, but fuel consumption also increases. Lean mixture + late ignition : high exhaust temperatures, but loss in power output 6

7 Exhaust Gas Treatment Catalytic converters Oxidizing catalysts for HC and CO Reducing catalysts for NOx Three-way catalysys for all three pollutants Catalytic Converters 7

8 Catalytic Converters Catalytic Converters 8

9 Catalytic Converters Exhaust Gas Treatment C m H n + [m+n/4] O 2 m CO 2 + n/2 H 2 O (1) CO + ½ O 2 CO 2 (2) H 2 + ½ O 2 H 2 O (3) CO + NO ½N 2 + CO 2 (4) C m H n + 2 [m+n/4] NO [m+n/4] N 2 + n/2 H 2 O + m CO 2 (5) H 2 + NO ½N 2 + H 2 O (6) SO 2 + ½ O 2 SO 3 (7) 5/2 H 2 + NO NH 3 + H 2 O (8) SO H 2 H 2 S + 2 H 2 O (9) NH 3 + CH 4 HCN + 3 H 2 (10) CO + H 2 O CO 2 + H 2 (11) CH n + 2 H 2 O CO 2 + [2+n/2] H 2 (12) 9

10 Exhaust Gas Treatment CO + ½ O 2 CO 2 (2) CO + NO ½N 2 + CO 2 (4) In lean mixtures reaction (2) is dominant O2 is present CO is reduced by oxidation and insufficient CO for the relatively slow reaction(4). CO + H 2 O CO 2 + H 2 (11) CH n + 2 H 2 O CO 2 + [2+n/2] H 2 (12) In rich mixtures reactions (11) and (12) have to be faster. Exhaust Gas Treatment 10

11 Emission Regulations Road Simulations Emission Regulations Exhaust Gas Emissions 11

12 Emission Regulations Chasis Dynamometers Emission Regulations Chasis Dynamometer 12

13 Emission Regulations Chasis Dynamometer Emission Regulations Exhaust Gas Emissions 13

14 Emission Regulations SHED Test 14